332 SCHOOL ENTOMOLOGY 



Whale-oil or fish-oil soap has been used extensively against 

 scale insects and plant lice, particularly by nurserymen and 

 florists. The best brands are made from caustic potash 

 rather than caustic soda and should not contain over 30 

 per cent of water. For most aphides one pound to six 

 gallons is effective. 



Pyrethrum, Buhach, or Persian insect powder, is made by 

 pulverizing the petals of the pyre thrum blossom, and kills 

 insects by clogging their breathing pores. It is used chiefly 

 for household pests and in greenhouses and small gardens. 

 It deteriorates rapidly with age and should be kept in tight 

 cans. On this account large users buy directly from the 

 only American manufacturers, the Buhach Producing Co., 

 Stockton, Cal. It may be used as a dry powder, pure or 

 diluted with flour, or in water at the rate of one ounce to 

 two gallons, which should stand a day before using. For 

 immediate use it should be boiled for five or ten minutes. 

 It is often burned in rooms to destroy mosquitoes and flies ; 

 as it leaves no odor after the room has been aired. 



Tobacco. A tobacco decoction may be made by steeping 

 tobacco leaves, stems, or refuse in water at the rate of 1 

 pound to 1 or 2 gallons, and then diluting for use according 

 to the strength of the tobacco and the insect to be combated. 

 Tobacco decoction is much used for dipping plants infested 

 with aphides and as a spray against aphides and similar soft- 

 bodied insects. Various extracts and solutions of tobacco 

 are now manufactured for use against plant lice, among the 

 best of which is "Black-leaf 40" or Nicotine Sulphate, and 

 are more satisfactory than home-made solutions on account 

 of their uniform strength. Tobacco dust has been widely 

 used against root-feeding aphides by removing the surface 

 soil and applying a liberal dressing and then covering. The 

 rains leaching through the tobacco carry the tobacco 



